Is there a way to catch all exceptions?

Questions
1

When I write

try do
   ...
catch
  _ -> do
    ...

I get error

Ambiguous type variable ‘e0’ arising from a use of ‘DA.Internal.Desugar.fromAnyException’
      prevents the constraint ‘(DA.Internal.Desugar.HasFromAnyException
                                  e0)’ from being solved.

Is there any way to catch all, or do I have to explicitly list all options?

2

No, you can only catch specific exception types atm. see below

3

Apologies, I blanked for a minute, that was completely wrong. You can catch AnyException to catch everything. To convert to a specific exception type afterwards use fromAnyException, .eg.

module Main where

import DA.Assert
import Daml.Script

f : () -> Script Text
f () = 
  try do
    x <- fail "abc"
    pure "unreachable"
  catch
    (ex : AnyException) -> pure "caught"

test = do
  x <- f () 
  x === "caught"
2 Likes
4

Is there a way to get the text of the exception when catching it generically?
E.g., the following naive approach didn’t work:

module Main where

import DA.Assert
import Daml.Script

f : () -> Script Text
f () = 
  try do
    x <- fail "abc"
    pure "unreachable"
  catch
    (ex : AnyException) -> pure ex.message

test = do
  x <- f () 
  x === "caught"
5

message is not a record field here. It’s a method of the HasMessage typeclass implemented by all exceptions. So you want something like this:

message ex
1 Like
6

@Arne_Gebert
To add to @cocreature 's reply, the value of x in your test will be “abc”, not “caught”. Try the following

f : () -> Script Text
f () = do
  try do
    x <- fail "abc"
    pure "unreachable"
  catch
    (ex : AnyException) -> pure $ message ex

test : Script ()
test = do
  x <- f () 
  x === "abc"
  pure ()
1 Like